I was considering ordering from overseas, but will they pass the customs? They do have ''fake'' cartridges in them:

Just to clear the confusion here. YES you *can* import them legally. BUT they are a bit of a questionable item (just like mock suppressors) and *may* be held/inspected longer if it comes to that (AFAIK agents will tend to err on the side of caution and send it to a supervisor if they're not sure of the legality of entrance for an item).